1. Field of the Invention
This invention relates to methods and apparatuses to treat intervertebral disc problems using percutaneous techniques without the need for major surgical intervention and more particularly to modify intervertebral disc tissue using controlled thermal energy, especially a resistive heater.
2. Description of Related Art
Intervertebral disc abnormalities have a high incidence in the population and may result in pain and discomfort if they impinge on or irritate nerves. Disc abnormalities may be the result of trauma, repetitive use, metabolic disorders and the aging process and include such disorders but are not limited to degenerative discs with (i) localized tears or fissures in the annulus fibrosus, (ii) localized disc herniations with contained extrusions, and (iii) chronic, circumferential bulges.
Disc fissures and tears result from structural degeneration (a part of the aging process that may be accelerated by trauma) of fibrous components of the annulus fibrosus. Even sneezing, bending or just attrition can tear these degenerated annulus fibers, creating a fissure. The fissure itself may be the sole morphological change, above and beyond generalized degenerative changes in the connective tissue of the disc. Biochemicals contained within the nucleus pulposus are alleged to escape through the fissure and irritate nearby structures. Fissures of the annulus can be debilitatingly painful. The fissure may be associated with a herniation of that portion of the annulus.
With a contained disc herniation, the nucleus pulposus works its way partly through the wall but is still contained within the annulus or beneath the posterior longitudinal ligament, and there are no free disc fragments in the spinal canal. Nevertheless, even a contained disc herniation is problematic because the outward protrusion can press on the spinal nerves or irritate other structures.
Another disc problem occurs when the disc bulges outward circumferentially in all directions and not just in one location. This occurs when over time the disc weakens, bulges outward and takes on a "roll" shape. Mechanical stiffness of the joint is reduced and the joint may become unstable. One vertebra may eventually settle on top of another. This problem continues as the body ages and accounts for shortened stature in old age. With the increasing life expectancy of the population, such degenerative disc disease and impairment of nerve function are becoming major public health problems. As the disc "roll" extends beyond the normal circumference, the disc height may be compromised which compresses vertebral foramina with sensitive nerves. In addition, osteophytes may form on the outer surface of the disc roll and further encroach on the spinal canal and nerve foramina. This condition is called lumbar spondylosis.
It has been thought that disc degeneration causes pain predominantly via segmental instability which disturbs sensitive structures which in turn register pain. Traditional, conservative methods of treatment include bed rest, pain and muscle relaxant medication, physical therapy and steroid injection. Upon failure of conservative therapy, spinal pain (assumed to be due to instability) has been treated by spinal fusion, which causes the vertebrae above and below the disc to grow solidly together and form a single, solid piece of bone. Fusion may be performed with or without instrumentation. Other treatments include discectomy alone or disc decompression with or without fusion. Disc decompression is performed to reduce pressure on the annulus (and its outward protrusion) by removing some of the nucleus contents by percutaneous nuclectomy. Surgical complications include disc space infection, nerve root injury, hematoma formation, collapse of the disc from decrease in height, and instability of the adjacent vertebrae.
These interventions have been problematic in that alleviation of back pain is unpredictable even if surgery is successful. In attempts to overcome these difficulties, new devices have been introduced to the market, including but not limited to pedicle screws and interbody fusion cages. Although pedicle screws provide a high fusion success rate, there is still no direct correlation between fusion success rate and patient improvement in function and pain. Studies on fusion have demonstrated success rates of between 50% and 67% for pain improvement. And a significant number of patients have more pain postoperatively. Therefore, different methods of helping patients with degenerative disc problems need to be explored.
FIGS. 1(a) and 1(b) illustrate a cross-sectional anatomical view of a vertebra and associated disc and a lateral view of a portion of a lumbar and thoracic spine, respectively. Structures of a typical cervical vertebra (superior aspect) are shown in FIG. 1(a): 104--lamina; 106--spinal cord; 108--dorsal root of spinal nerve; 114--ventral root of spinal nerve; 116--posterior longitudinal ligament; 118--intervertebral disc; 120--nucleus pulposus; 122--annulus fibrosus; 124--anterior longitudinal ligament; 126--vertebral body; 128--pedicle; 130--vertebral artery; 132--vertebral veins; 134--superior articular facet; 136--posterior lateral portion of the annulus; 138--posterior medial portion of the annulus; 142--spinous process; and 144--dura mater. In FIG. 1(a), half of the intervertebral disc 118 has been cut away so that half of the vertebral body 126 can be seen. FIG. 1(b) is a lateral aspect of the lower portion of a typical spinal column showing the entire lumbar region and part of the thoracic region showing the following structures: 118--intervertebral disc; 126--vertebral body; 142--spinous process; 168--inferior articular process; 170--inferior vertebral notch; 110--spinal nerve; 174--superior articular process; 176--lumbar curvature; and 180--sacrum.
The presence of the spinal cord or nerve sac and the posterior portion of the vertebral body, including the spinous process, lamina and superior and inferior articular processes, prohibit introduction of a needle or trocar from a directly posterior position. This is important because the posterior disc wall is the site of symptomatic annulus tears or disc protrusions/extrusions that compress or irritate spinal nerves for most degenerative disc syndromes. The inferior articular process 168, along with the pedicle 128 and the lumbar spinal nerve 110, form a small "triangular" window (shown in black in FIG. 1(c)) through which needle introduction can be achieved from the posterior lateral position. FIG. 1(d) is a cross-sectional view of the lower back with an instrument introduced by the posterior lateral approach. It is well known to those skilled in the art that percutaneous access to the disc is achieved by placing an introducer into the disc from this posterior lateral approach, but the triangular window does not allow much room to maneuver. Once the introducer pierces the tough annulus fibrosus, the introducer is fixed at two points along its length and has very little freedom of movement. Thus, this approach has allowed access only to small central and anterior portions of the nucleus pulposus. Current methods do not permit percutaneous access to the posterior half of the nucleus or to the posterior wall of the disc. Major and potentially dangerous surgery would be required to access these areas.
U.S. Pat. No. 5,433,739 (the "'739 patent") discloses placement of an RF electrode in an interior region of the disc approximately at the center of the disc. RF power is applied, and heat then putatively spreads out globally throughout the disc. The '739 patent teaches the use of a rigid shaft which includes a sharpened distal end that penetrates through the annulus fibrosus and into the nucleus pulposus. In one embodiment the shaft has to be rigid enough to permit the distal end of the RF electrode to pierce the annulus fibrosus, and the ability to maneuver its distal end within the nucleus pulposus is limited. In another embodiment, a somewhat more flexible shaft is disclosed. However, the embodiments of the '739 patent do not permit access to the posterior, posterior lateral and posterior medial region of the disc, nor do they provide for focal delivery of therapy to a selected local region within the disc or precise temperature control at the annulus. The '739 patent teaches the relief of pain by globally heating the disc. It does not disclose contraction or tightening of a herniated or bulging disc or treating of an annular fissure.
U.S. Pat. No. 5,201,729 (the "'729 patent") discloses the use of an optical fiber that is introduced into a nucleus pulposus. In the '729 patent, the distal end of a stiff optical fiber shaft extends in a lateral direction relative to a longitudinal axis of an introducer. This prevents delivery of coherent energy into the nucleus pulposus in the direction of the longitudinal axis of the introducer. Due to the limited access from the posterior lateral approach, stiff shaft, and lateral energy delivery, the device of the '729 patent is unable to gain close proximity to any selected portion of the annulus (i.e., posterior, posterior medial and central posterior locations) requiring treatment or to precisely control temperature in the nucleus at this location. The '729 patent teaches the use of coherent energy to vaporize the nucleus pulposus, which by the nature of the technique generates very high temperatures. No treatment of annular herniations or disc bulges is disclosed.
Accordingly, it is desirable to treat disc abnormalities at locations previously not accessible via percutaneous procedures without substantial destruction to the disc. It would be further desirable to provide controllable thermal energy to the posterior nucleus pulposus and the posterior, posterior lateral and the posterior medial regions of the inner wall of the annulus fibrosus without heating other regions of the nucleus, as would occur with prior art heating elements.